In prior wind turbine blade fabrication, fiber layers such as glass or carbon fabric are laid in a horizontally oriented suction-side mold. Mandrels representing the internal void geometry of the blade are placed on this suction side layup. The fabric is then wrapped around the leading edge and pressure side of the mandrel to meet itself at the trailing edge. This makes a closed C-shaped layup with one seam at the trailing edge. A pressure side mold cover is then closed over the layup. The fabric is infused with a matrix material such as epoxy or thermosetting polymer before or after the layup steps and closing of the mold. The mandrels may be inflatable or solid, or they may have a rigid core covered with a compressible material such as foam to press the layup against the interior surfaces of the mold, as taught for example in U.S. Pat. No. 8,007,624 B2, incorporated by reference herein.
However, the mandrel may shift position while the layup is being placed on it or while the mold is closing. This occurs mostly in areas of high curvature, resulting in wrinkles and areas of enriched resin, both of which degrade structural integrity and must be repaired after the blade is removed from the mold. If the mandrel shifts too much, it can become stuck inside the blade. Mandrel shifting is possible, in part, because the air in the inflatable or foam parts can shift peripherally and/or diagonally to other locations of the mandrel cross-section. This allows the mandrel shape to be insufficiently maintained.